Why can I no longer transfer files to LG G3, from laptop (Windows XP)?

[AC Question]

Suddenly can no longer transfer files to LG G3, from laptop (Windows XP)

Have always been able to transfer (copy) audio books (MP3) from my laptop to Android mobile phone. Now I get error message that connection has been broken, but it hasn't - I can still open files on the phone from the laptop in Windows Explorer.